The block copolymer has a molecular structure in which polymer blocks having different chemical structures from one another are connected to one another by covalent bonds. The block copolymer can form a regularly arranged structure, such as a sphere, a cylinder and a lamella, by phase separation. The size of a domain that is formed by the self-assembly phenomenon of a block copolymer can be adjusted over a wide range, and the domain can be produced into various structures which can be applied to the production of a variety of next-generation nanodevices, magnetic storage media, and patterns (by lithography or the like), for example, the formation of high-density magnetic recording media, nanowires, quantum dots, or metal dots.